1. Field of the Invention
The present invention relates to a method for manufacturing a light-emitting element in which a layer comprising an organic compound is sandwiched between a pair of electrodes, and a light-emitting element formed by the method for manufacturing.
2. Description of the Related Art
A light-emitting element typified by an organic electroluminescent (EL) element has a typical structure in which a layer comprising an organic compound is sandwiched between a pair of electrodes, and it is an element which emits light by applying voltage to the both electrodes. In the light-emission mechanism, when the voltage is applied to the electrodes, a hole from an anode and an electron from a cathode are injected into the layer comprising an organic compound and moved. It is said that the hole and the electron cause a recombination with a certain probability and a singlet exciton of the organic compound is generated to emit light. Light-emission of an organic electroluminescent element can pass through an anode and a substrate to be emitted outside by using a transparent electrode as the anode.
Various studies for improving the luminous efficiency of an organic EL element has been made for the sake of utilizing an organic EL element as a display element of a display unit. It is one of important objects to increase the light-extraction efficiency (a coefficient of taking out light-emission in the interior of an element) in order to increase the luminous efficiency.
The light-extraction efficiency is a value that is obtained by considering the total reflection in an organic layer, on an electrode interface or the like with respect to light emission from the inside of the organic layer, but it is thought that the limit to the light-extraction efficiency is about 20 percents in view of a refractive index of the organic layer.
It is described in Reference 1 (Japanese Patent Laid-Open No. 2002-110363) that a direction of light-emission from an organic compound included in a light emitting layer is turned to an electrode direction (light-emission from an organic compound is controlled by a molecular arrangement), which is effective for preventing a loss of light-emission by the light-extraction efficiency.
However, there is a risk that an organic compound is damaged since a rubbing treatment is performed on a surface of an organic layer formed over a substrate, according to the method described in Reference 1.